1. Technical Field
The present invention relates to a control device for an electric motor and related method.
2. Description of the Related Art
A direct current brushless motor consists of a permanent magnet and of a stator consisting of a certain number of windings (generally three) that are normally star or polygon connected (for example triangle or delta connected). The windings are driven through a driving circuit the output stage of which generally comprises a half bridge (two bipolar or MOS transistors) for each winding.
FIG. 1 shows a typical circuit diagram of an output stage 1 and a motor 2 connected thereto with three configured star phases; the motor is indicated by three star-connected windings La, Lb and Lc. Detecting the rotor position during rotation generally requires the output stage of a winding of the motor to be placed in high impedance status, for example the output stage of the winding La, and a circuit 3 to be used that is suitable for detecting a Pbemf signal that represents the polarity of the induced back electromotive force (BEMF) of said winding in order to be able to detect the zero crossing (Zero Crossing or ZC) of the BEMF. This is an indication of the instantaneous position of the rotor, whilst speed is calculated simply as the temporal distance of the last two ZC readings. These data are thus those used for driving the motor in a synchronous manner.